>>149227687
You can't really pick just one but I'm partial to Avengers #229. That whole story to start is I think the best Pym story ever and it does am elegant job of finishing off the storyline that Shooter left on with him in a way that makes Pym a more interesting character. And that specific issue gives us what's probably Pym's greatest moment where he defeats the entire Masters of Evil singlehandedly and captured using his wits.